基准面偏移沙盒

A geodetic datum is a reference system for measuring locations on Earth. Different datums use different reference ellipsoids and origins.

WGS84 is the global standard used by GPS. NAD83 is used for most modern North American surveys. NAD27 was the historical US standard.

The same physical location will have slightly different coordinates in different datums. NAD27 to WGS84 shifts can be 10-100+ meters in North America.